System and method for providing blood pressure safe zone indication during autoregulation monitoring

ABSTRACT

A method for monitoring autoregulation includes, using a processor, using a processor to execute one or more routines on a memory. The one or more routines include receiving one or more physiological signals from a patient, determining a correlation-based measure indicative of the patient&#39;s autoregulation based on the one or more physiological signals, and generating an autoregulation profile of the patient based on autoregulation index values of the correlation-based measure. The autoregulation profile includes the autoregulation index values sorted into bins corresponding to different blood pressure ranges. The one or more routines also include designating a blood pressure range encompassing one or more of the bins as a blood pressure safe zone indicative of intact regulation and providing a signal to a display to display the autoregulation profile and a first indicator of the blood pressure safe zone.

BACKGROUND

The present disclosure relates generally to medical devices and, moreparticularly, to systems and methods for monitoring autoregulation.

This section is intended to introduce the reader to various aspects ofart that may be related to various aspects of the present disclosure,which are described and/or claimed below. This discussion is believed tobe helpful in providing the reader with background information tofacilitate a better understanding of the various aspects of the presentdisclosure. Accordingly, it should be understood that these statementsare to be read in this light, and not as admissions of prior art.

In the field of medicine, medical professionals often desire to monitorcertain physiological parameters of their patients. In some cases,clinicians may wish to monitor a patient's autoregulation.Autoregulation is a physiological process that attempts to maintain anoptimal cerebral blood flow to supply appropriate levels of oxygen andnutrients to the brain. During autoregulation, cerebral arteriolesdilate or constrict to maintain optimal blood flow. For example, ascerebral pressure decreases, cerebral arterioles dilate in an attempt tomaintain blood flow. As cerebral pressure increases, cerebral arteriolesconstrict to reduce the blood flow that could cause injury to the brain.If the patient's autoregulation process is not functioning properly, thepatient may experience inappropriate cerebral blood flow, which may havenegative effects on the patient's health. In particular, a drop incerebral blood flow may cause ischemia, which may result in tissuedamage or death of brain cells. An increase in cerebral blood flow maycause hyperemia, which may result in swelling of the brain or edema.

Some existing systems for monitoring autoregulation may determine apatient's autoregulation status based on various physiological signals.However, existing systems may not provide the patient's autoregulationstatus and/or changes in the patient's autoregulation status in aneffective manner.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the disclosed techniques may become apparent upon readingthe following detailed description and upon reference to the drawings inwhich:

FIG. 1 is a block diagram of an embodiment of a system for monitoring apatient's autoregulation;

FIG. 2 is an example of a display configured to display anautoregulation status of a patient (e.g., having a blood pressure safezone);

FIG. 3 is an example of a display configured to display anautoregulation status of a patient (e.g., having a preliminary bloodpressure safe zone);

FIG. 4 is a process flow diagram of a method of monitoringautoregulation that includes designating a blood pressure safe zone, inaccordance with an embodiment;

FIG. 5 is a process flow diagram of a method of monitoringautoregulation that includes determining how to designate a bloodpressure safe zone, in accordance with an embodiment;

FIG. 6 is an example of a graph illustrating a regional oxygensaturation (rSO₂)-blood pressure (BP) curve derived from regional oxygensaturation values and blood pressure values (e.g., having a target bloodpressure derived from the rSO₂-BP curve);

FIG. 7 is an example of a graph illustrating an rSO₂-BP curve derivedfrom regional oxygen saturation values and blood pressure values (e.g.,having a target blood pressure derived from gradients of the rSO₂-BPcurve);

FIG. 8 is a process flow diagram of a method of determining a targetblood pressure utilizing characteristics (e.g., gradients) of an rSO₂-BPcurve derived from regional oxygen saturation values and blood pressurevalues, in accordance with an embodiment;

FIG. 9 is an example of a graph illustrating an rSO₂-BP curve derivedfrom regional oxygen saturation values and blood pressure values (e.g.,having a target blood pressure derived from errors associated with therSO₂-BP curve); and

FIG. 10 is an example of a graph illustrating an rSO₂-BP curve derivedfrom regional oxygen saturation values and blood pressure values (e.g.,having a target blood pressure derived from a point of inflection of therSO₂-BP curve).

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

One or more specific embodiments of the present techniques will bedescribed below. In an effort to provide a concise description of theseembodiments, not all features of an actual implementation are describedin the specification. It should be appreciated that in the developmentof any such actual implementation, as in any engineering or designproject, numerous implementation-specific decisions must be made toachieve the developers' specific goals, such as compliance withsystem-related and business-related constraints, which may vary from oneimplementation to another. Moreover, it should be appreciated that sucha development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure.

A physician may monitor a patient's autoregulation through the use ofvarious monitoring devices and systems. In some cases, a patient'sautoregulation may be monitored via correlation-based measures (e.g.,autoregulation indices) indicative of the patient's autoregulationfunction. For example, near-infrared spectroscopy (NIRS)-based indicesmay be utilized as measures of autoregulation. Autoregulation may bemonitored by correlating measurements of the patient's blood pressure(e.g., arterial blood pressure) with measurements of the patient'soxygen saturation (e.g., regional oxygen saturation). In particular, acerebral oximetry index (COx) indicative of the patient's autoregulationstatus may be derived based at least in part on a linear correlationbetween the patient's blood pressure and oxygen saturation. In addition,autoregulation may be monitored by correlating measurements of thepatient's blood pressure with measurements of blood flow. In particular,a hemoglobin volume index (HVx) indicative of the patient'sautoregulation may be derived based at least in part on a linearcorrelation between the patient's blood pressure and blood flow.Further, non-NIRS-based indices may be utilized as measures ofautoregulation, such as mean velocity index (Mx).

The disclosed systems and methods may utilize an autoregulation index togenerate and display an autoregulation profile (e.g., autoregulationindex values sorted into bins corresponding to different blood pressureranges) of the patient. The measures of autoregulation may be NIRS-basedindices (e.g., COx, HVx, etc.) or non-MRS-based indices (e.g., Mx)utilized by the systems and methods. The autoregulation profile mayinclude the autoregulation plotted on a vertical axis and the bloodpressures plotted on the horizontal axis. A negative autoregulationindex value may indicate intact autoregulation within a particular bloodpressure range, while a positive autoregulation index value may indicateimpaired autoregulation within a particular blood pressure range. Inaddition, the system may generate a blood pressure (BP) safe zone (i.e.,designate a blood pressure range encompassing one or more of the bins)indicative of intact autoregulation. If there is insufficient patientdata (e.g., autoregulation index measurements and blood pressuremeasurements) of the patient, an initial BP safe zone may be generatedutilizing historical population data (e.g., based on patient specificinputs) and/or initially measured baseline physiological parameters(e.g., mean arterial pressure (MAP), heart rate, respiration rate,regional oxygen saturation (rSO₂), etc.) of the patient. Once there issufficient patient data, a patient specific BP safe zone may begenerated based on the patient's autoregulation index measurements andblood pressure measurements. A graphical indicator of the BP safe zonemay be overlaid on the corresponding one or more bins of theautoregulation profile. If the patient's current blood pressuremeasurement falls outside of the zone, the system may provide an alarm(e.g., audible or visual indication).

The system may display other information along with the autoregulationprofile and the BP safe zone. For example, a BP history may bedisplayed. The BP history may include bins of blood pressure rangescorresponding to the bins in the autoregulation profile plotted on ahorizontal axis and a count relating to time spent in (or out of) the BPsafe zone on a vertical axis. The count may represent an amount orpercentage of time in the BP safe zone, a number of times in the BP safezone, or a number of times out of the BP safe zone. In certainembodiments, the graphical indicator of the BP safe zone may alsooverlay the bins of BP history that correspond to the bins of theautoregulation profile within the BP safe zone. In addition, the systemmay display a BP signal (e.g., plot of a BP signal segment (i.e., BPvalue over time)).

The system may also display an indicator of a target blood pressure(TBP). The TBP may represent a blood pressure value or a range of valuesat which the patient's autoregulation function is greatest and/or may beuseful for clinical management of a patient's blood pressure. Forexample, the target blood pressure may guide a healthcare provider'streatment of the patient (e.g., provide an indication of whether thehealthcare provider should administer medication to lower the patient'sblood pressure or to raise the patient's blood pressure to reach the TBPwithin the intact autoregulation zone). For example, the TBP may bedisplayed in a variety of ways (e.g., point, number, vertical line,etc.). In certain embodiments, the system may indicate a distance of thepatient's measured blood pressure from the TBP. The distance may beindicated via a gradiated color change of the indicator of the TBP or ablip bar.

In certain embodiments, the TBP is provided to the system. In otherembodiments, the system generates the TBP. In certain situations, it maybe beneficial to identify autoregulation zones indicative of a patient'sblood pressure dependent autoregulation status. A patient'sautoregulation system may typically function well over a certain rangeof blood pressures. Accordingly, each patient typically exhibits atleast three autoregulation zones: a lower impaired autoregulation zoneassociated with relatively low blood pressures at which the patient'sautoregulation function is impaired, an intact autoregulation zoneassociated with intermediate blood pressures at which the patient'sautoregulation system works properly, and an upper impairedautoregulation zone associated with relatively high blood pressures atwhich the patient's autoregulation function is impaired. For example,although the blood pressures at which the autoregulation systemfunctions properly may vary by patient, a particular patient may exhibita lower impaired autoregulation zone associated with relatively lowblood pressures of less than approximately 60 mmHg at which thepatient's autoregulation function is impaired, an intact autoregulationzone associated with intermediate blood pressures between approximately60 and 150 mmHg at which the patient's autoregulation system worksproperly, and an upper impaired autoregulation zone associated withrelatively high blood pressures above approximately 150 mmHg at whichthe patient's autoregulation function is impaired. It may beadvantageous to identify the patient's autoregulation zones and/or todetermine an upper limit of autoregulation (ULA) value and/or a lowerlimit of autoregulation (LLA) that approximately define an upper and alower blood pressure (e.g., MAP) boundary, respectively, within whichautoregulation is generally intact and functioning properly. Bloodpressures approximately above the ULA and/or approximately below the LLAmay be associated with impaired autoregulation function.

In some embodiments, the systems and methods may be configured todetermine a TBP for the patient based on an rSO₂-BP curve, the LLA,and/or ULA. In some embodiments, the TBP may be a blood pressure valuealong the rSO₂-BP curve equidistant from the LLA and ULA within theintact autoregulation zone. In other embodiments, the TBP may be a pointof the rSO₂-BP curve within the intact autoregulation zone closest toeither the LLA or the ULA depending on if the clinical consequenceswould be worse dropping below the LLA or exceeding the ULA.Alternatively, the TBP may be determined based on the gradients of therSO₂-BP curve (e.g., gradient of the curve blow the LLA and/or thegradient of the curve above the ULA). In some embodiments, the TBP maybe determined based on error bars associated within the LLA and/or ULA.In other embodiments, the TBP may be determined by a point ofinflection.

As discussed in more detail below, the systems and methods may beconfigured to utilize the BP safe zone and/or the TBP. In someembodiments, the system may be configured to provide informationindicative of the autoregulation status, the BP safe zone, and/or theTBP to an operator. Such systems and methods may in turn provideimproved patient monitoring and patient care.

FIG. 1 is a block diagram of an embodiment of a system 10 for monitoringa patient's autoregulation. As shown, the system 10 includes a bloodpressure sensor 12, an oxygen saturation sensor 14 (e.g., a regionaloxygen saturation sensor), a controller 16, and an output device 18. Theblood pressure sensor 12 may be any sensor or device configured toobtain the patient's blood pressure (e.g., MAP). For example, the bloodpressure sensor 12 may include a blood pressure cuff for non-invasivelymonitoring blood pressure or an arterial line for invasively monitoringblood pressure. In certain embodiments, the blood pressure sensor 12 mayinclude one or more pulse oximetry sensors. In some such cases, thepatient's blood pressure may be derived by processing time delaysbetween two or more characteristic points within a singleplethysmography (PPG) signal obtained from a single pulse oximetrysensor. Various techniques for deriving blood pressure based on acomparison of time delays between certain components of a single PPGsignal obtained from a single pulse oximetry sensor is described in U.S.Publication No. 2009/0326386, entitled “Systems and Methods forNon-Invasive Blood Pressure Monitoring,” the entirety of which isincorporated herein by reference. In other cases, the patient's bloodpressure may be continuously, non-invasively monitored via multiplepulse oximetry sensors placed at multiple locations on the patient'sbody. As described in U.S. Pat. No. 6,599,251, entitled “ContinuousNon-invasive Blood Pressure Monitoring Method and Apparatus,” theentirety of which is incorporated herein by reference, multiple PPGsignals may be obtained from the multiple pulse oximetry sensors, andthe PPG signals may be compared against one another to estimate thepatient's blood pressure. Regardless of its form, the blood pressuresensor 12 may be configured to generate a blood pressure signalindicative of the patient's blood pressure (e.g., arterial bloodpressure) over time. As discussed in more detail below, the bloodpressure sensor 12 may provide the blood pressure signal to thecontroller 16 or to any other suitable processing device to enableidentification of the autoregulation zone(s) and to enable evaluation ofthe patient's autoregulation status.

As shown, the oxygen saturation sensor 14 may be a regional oxygensaturation sensor configured to generate an oxygen saturation signalindicative of blood oxygen saturation within the venous, arterial, andcapillary systems within a region of the patient. For example, theoxygen saturation sensor 14 may be configured to be placed on thepatient's forehead and may be used to calculate the oxygen saturation ofthe patient's blood within the venous, arterial, and capillary systemsof a region underlying the patient's forehead (e.g., in the cerebralcortex). In such cases, the oxygen saturation sensor 14 may include anemitter 20 and multiple detectors 22. The emitter 20 may include atleast two light emitting diodes (LEDs), each configured to emit atdifferent wavelengths of light, e.g., red or near infrared light. Theemitter 20 may be driven to emit light by light drive circuitry of amonitor (e.g., a specialized monitor having a controller configured tocontrol the light drive circuitry). In one embodiment, the LEDs of theemitter 20 emit light in the range of about 600 nm to about 1000 nm. Ina particular embodiment, one LED of the emitter 20 is configured to emitlight at about 730 nm and the other LED of the emitter 20 is configuredto emit light at about 810 nm. One of the detectors 22 is positionedrelatively “close” (e.g., proximal) to the emitter 20 and one of thedetectors 22 is positioned relatively “far” (e.g., distal) from theemitter 22. Light intensity of multiple wavelengths may be received atboth the “close” and the “far” detectors 22. For example, if twowavelengths are used, the two wavelengths may be contrasted at eachlocation and the resulting signals may be contrasted to arrive at aregional saturation value that pertains to additional tissue throughwhich the light received at the “far” detector passed. Surface data(e.g., from the skin) may be subtracted out, to generate a regionaloxygen saturation (rSO₂) signal for the target tissues over time. Asdiscussed in more detail below, the oxygen saturation sensor 14 mayprovide the regional oxygen saturation signal to the controller 16 or toany other suitable processing device to enable evaluation of thepatient's autoregulation status. While the depicted oxygen saturationsensor 14 is a regional saturation sensor, the sensor 14 may be a pulseoximeter configured to obtain the patient's oxygen saturation or may beany suitable sensor configured to provide a signal indicative of thepatient's blood flow. For example, the sensor 14 may be configured toemit light at a single wavelength (e.g., an isobestic wavelength) and toprovide a signal indicative of blood flow.

In operation, the blood pressure sensor 12 and the oxygen saturationsensor 14 may each be placed on the same or different parts of thepatient's body. Indeed, the blood pressure sensor 12 and the oxygensaturation sensor 14 may in some cases be part of the same sensor orsupported by a single sensor housing. For example, the blood pressuresensor 12 and the oxygen saturation sensor 14 may be part of anintegrated oximetry system configured to non-invasively measure bloodpressure (e.g., based on time delays in a PPG signal) and regionaloxygen saturation. One or both of the blood pressure sensor 12 or theoxygen saturation sensor 14 may be further configured to measure otherparameters, such as hemoglobin, respiratory rate, respiratory effort,heart rate, saturation pattern detection, response to stimulus such asbispectral index (BIS) or electromyography (EMG) response to electricalstimulus, or the like. While an exemplary system 10 is shown, theexemplary components illustrated in FIG. 1 are not intended to belimiting. Indeed, additional or alternative components and/orimplementations may be used.

As noted above, the blood pressure sensor 12 may be configured toprovide the blood pressure signal to the controller 16, and the oxygensaturation sensor 14 may be configured to provide the oxygen saturationsignal to the controller 16. In certain embodiments, the controller 16is an electronic controller having electrical circuitry configured toprocess the various received signals. In particular, the controller 16may be configured to process the blood pressure signal and the oxygensaturation signal to determine the autoregulation zone(s) and/or toevaluate the patient's cerebral autoregulation status. Alternatively,the controller 16 may be configured to process the blood pressure signaland the blood volume signal to evaluate the patient's cerebralautoregulation status. In some embodiments, the controller 16 may bepart of a specialized monitor and/or may be configured to controloperation of (e.g., control light drive circuitry to drive the emitter20 of the oxygen saturation sensor 14) and/or receive signals directlyfrom the blood pressure sensor 12 and/or the oxygen saturation sensor14. Although the blood pressure sensor 12 and the oxygen saturationsensor 14 may be configured to provide their respective signals or datadirectly to the controller 16, in certain embodiments, the signals ordata obtained by the blood pressure sensor 12 and/or the oxygensaturation sensor 14 may be provided to one or more intermediateprocessing devices (e.g., specialized monitor, such as a blood pressuremonitor or an oxygen saturation monitor, or the like), which may in turnprovide processed signals or data to the controller 16.

The controller 16 may be configured to determine one or moreautoregulation index values (e.g., COx, HVx, etc.). In some embodiments,the controller 16 may be configured to determine a COx based on theblood pressure signal and the oxygen saturation signal. The COx isgenerally indicative of vascular reactivity, which is related tocerebral blood vessels' ability to control proper blood flow, viavasoconstriction (a narrowing of the blood vessel) and/or vasodilation(expansion of the blood vessel), for example. The controller 16 mayderive a COx value by determining a linear correlation between bloodpressure measurements and oxygen saturation measurements. The linearcorrelation may be based on a Pearson coefficient, for example. ThePearson coefficient may be defined as the covariance of the measuredblood pressure (e.g., arterial blood pressure or MAP) and oxygensaturation divided by the product of their standard deviations. Theresult of the linear correlation may be a regression line between theblood pressure measurements and the oxygen saturation measurements, andthe slope of the regression line may be generally indicative of thepatient's autoregulation status. In one possible implementation, aregression line with a relatively flat or negative slope (e.g., bloodpressure increases after regional oxygen saturation decreases) maysuggest that cerebral autoregulation is working properly, while aregression line with a positive slope (e.g., blood pressure remains thesame or decreases after regional oxygen saturation decreases) maysuggest that the cerebral autoregulation is impaired. Thus, if theregression line has negative slope, the COx value is between −1 and 0.If the regression line has a positive slope, the COx value is between 0and 1.

In some embodiments, the controller 16 may be configured to determine anHVx based on the blood pressure signal and the blood volume signal. TheHVx represents the relationship between relative tissue hemoglobin andMAP. HVx is based on the assumption that autoregulatory dilation andvasoconstriction produce changes in cerebral blood volume that areproportional to changes in relative tissue hemoglobin. The controller 16may derive an HVx value by determining a linear correlation betweenblood pressure measurements and blood volume measurements. The linearcorrelation may be based on a Pearson coefficient, for example. ThePearson coefficient may be defined as the covariance of the measuredblood pressure (e.g., arterial blood pressure or MAP) and oxygensaturation divided by the product of their standard deviations. Theresult of the linear correlation may be a regression line between theblood pressure measurements and the blood volume measurements, and theslope of the regression line may be generally indicative of thepatient's autoregulation status. In one possible implementation, aregression line with a relatively flat or negative slope (e.g., bloodpressure increases after blood volume decreases) may suggest thatcerebral autoregulation is working properly, while a regression linewith a positive slope (e.g., blood pressure remains the same ordecreases after blood volume decreases) may suggest that the cerebralautoregulation is impaired. Thus, if the regression line has negativeslope, the HVx value is between −1 and 0. If the regression line has apositive slope, the HVx value is between 0 and 1.

The controller 16 may be configured to generate and display (via anoutput device 18 such as a display) an autoregulation profile (e.g.,autoregulation index values sorted into bins corresponding to differentblood pressure ranges) of the patient based on the autoregulation indexvalues and the blood pressure measurements. The autoregulation profilemay include the autoregulation index values plotted on a vertical axisand the blood pressures plotted on the horizontal axis. A negativeautoregulation index value may indicate intact autoregulation within aparticular blood pressure range, while a positive autoregulation indexvalue may indicate impaired autoregulation within a particular bloodpressure range. In addition, the controller 16 may generate a BP safezone (i.e., designate a blood pressure range encompassing one or more ofthe bins) indicative of intact autoregulation. If there is insufficientpatient data (e.g., autoregulation index measurements and blood pressuremeasurements) of the patient, the controller 16 may generate an initialBP safe zone utilizing historical population data (e.g., based onpatient specific inputs such as age, sex, body mass index (BMI), etc.)and/or initially measured baseline physiological parameters (e.g., meanarterial pressure (MAP), heart rate, respiration rate, regional oxygensaturation (rSO₂), etc.) of the patient. Once there is sufficientpatient data, the controller 16 may generate a patient specific BP safezone based on the patient's autoregulation index measurements and bloodpressure measurements. A graphical indicator of the BP safe zone may beoverlaid the corresponding one or more bins of the autoregulationprofile.

The controller 16 may generate and display other information along withthe autoregulation profile and the BP safe zone. For example, a BPhistory may be displayed. The BP history may include bins of bloodpressure ranges corresponding to the bins in the autoregulation profileplotted on a horizontal axis and a count relating to time spent in (orout of) the BP safe zone on a vertical axis. The count may represent anamount or percentage of time in the BP safe zone, a number of times inthe BP safe zone, or a number of times out of the BP safe zone. Incertain embodiments, the graphical indicator of the BP safe zone mayalso overlay the bins of BP history that correspond to the bins of theautoregulation profile within the BP safe zone. In addition, thecontroller 16 may display a BP signal (e.g., plot of a BP signal segment(i.e., BP value over time)) via the output device 18 (e.g., display).

The controller 16 may also cause display of an indicator of TBP via theoutput device 18. The TBP may represent a blood pressure value or arange of values at which the patient's autoregulation function isgreatest and/or may be useful for clinical management of a patient'sblood pressure. For example, the target blood pressure may guide ahealthcare provider's treatment of the patient (e.g., provide anindication of whether the healthcare provider should administermedication to lower the patient's blood pressure or to raise thepatient's blood pressure to reach the TBP within the intactautoregulation zone). For example, the TBP may be displayed in a varietyof ways (e.g., point, number, vertical line, etc.). In certainembodiments, the controller 16 may indicate a distance of the patient'smeasured blood pressure from the TBP via the output device 18. Thedistance may be indicated via a gradiated color change (e.g., from greento amber to red, where green represents a closer distance, amber anintermediate distance, and red a farther distance) of the indicator ofthe TBP or a blip bar.

In certain embodiments, the controller 16 receives an input of the TBP.In other embodiments, the controller 16 (e.g., via algorithms) generatesthe TBP. In some embodiments, the controller 16 is configured todetermine the TBP for the patient based on an rSO₂-BP curve, the LLA,and/or ULA. In some embodiments, the TBP may be a blood pressure valuealong the rSO₂-BP curve equidistant from the LLA and ULA within theintact autoregulation zone. In other embodiments, the TBP may be a pointof the rSO₂-BP curve within the intact autoregulation zone closest toeither the LLA or the ULA depending on if the clinical consequenceswould be worse dropping below the LLA or exceeding the ULA.Alternatively, the TBP may be determined based the gradients of therSO₂-BP curve (e.g., gradient of the curve blow the LLA and/or thegradient of the curve above the ULA). In some embodiments, the TBP maybe determined based on error bars associated within the LLA and/or ULA.In other embodiments, the TBP may be determined by a point ofinflection.

In the illustrated embodiment, the controller 16 includes a processor 24and a memory device 26. The controller 16 may also include one or morestorage devices. As discussed in more detail below, the processor 24 maybe used to execute code stored in the memory device 26 or other suitablecomputer-readable storage medium or memory circuitry, such as code forimplementing various monitoring functionalities. The processor 24 may beused to execute software, such as software for carrying out any of thetechniques disclosed herein, such as processing the blood pressuresignals, blood volume signals, and/or oxygen saturation signals,determining a COx value, determining a HVx value, determining the TBP,identifying autoregulation zones, identifying the LLA and/or the ULA,causing display of information related to the autoregulation profile,the BP history, the BP safe zone, and/or the status on a display, and soforth. Moreover, the processor 24 may include multiple microprocessors,one or more “general-purpose” microprocessors, one or morespecial-purpose microprocessors, and/or one or more application specificintegrated circuits (ASICS), or some combination thereof. For example,the processor 24 may include one or more reduced instruction set (RISC)processors.

The memory device 26 may include a volatile memory, such as randomaccess memory (RAM), and/or a nonvolatile memory, such as ROM. Thememory device 26 may include one or more tangible, non-transitory,machine-readable media collectively storing instructions executable bythe processor 24 to perform the methods and control actions describedherein. Such machine-readable media can be any available media that canbe accessed by the processor 24 or by any general purpose or specialpurpose computer or other machine with a processor. The memory device 26may store a variety of information and may be used for various purposes.For example, the memory device 26 may store processor-executableinstructions (e.g., firmware or software) for the processor 24 toexecute, such as instructions for processing the blood pressure signals,blood volume signals, and/or oxygen saturation signals, determining aCOx value, determining a HVx value, determining the TBP, identifyingautoregulation zones, identifying the LLA and/or the ULA, causingdisplay of information related to the autoregulation profile, the BPhistory, the BP safe zone, and/or the status on a display, and so forth.The storage device(s) (e.g., nonvolatile storage) may include read-onlymemory (ROM), flash memory, a hard drive, or any other suitable optical,magnetic, or solid-state storage medium, or a combination thereof. Thestorage device(s) may store data (e.g., the blood pressure signal, theblood pressure signal, the oxygen saturation signal, the COx, the HVx,the BP safe zone, the autoregulation profile, the BP history, the TBP,etc.), instructions (e.g., software or firmware for processing the bloodpressure signals, blood volume signals, and/or oxygen saturationsignals, determining a COx value, determining a HVx value, determiningthe TBP, identifying autoregulation zones, identifying the LLA and/orthe ULA, causing display of information related to the autoregulationprofile, the BP history, the BP safe zone, and/or the status on adisplay, and so forth), predetermined thresholds, and any other suitabledata.

As shown, the system 10 includes the output device 18. In someembodiments, the controller 16 may be configured to provide signalsindicative of the autoregulation profile, the BP history, the BP safezone, the TBP, the current blood pressure, the distance of current bloodpressure from the TBP, and/or the patient's autoregulation status (e.g.,current blood pressure relative to the BP safe zone) to the outputdevice 18. As discussed in more detail below, the controller 16 may beconfigured to generate an alarm signal indicative of the patient'sautoregulation status and to provide the alarm signal to the outputdevice 18. For example, in certain embodiments, if the current bloodpressure of the patient falls outside of the BP safe zone, thecontroller 16 may provide an alarm (e.g., audible or visual indication)via the output device 18. In certain embodiments, the alarm may beprovided via the flashing of portions of the display (e.g., theautoregulation profile, the BP safe zone, the BP history, and/or the BPsignal). The alarm may also be provided via changing a color of the BPsafe zone indicative of a blood pressure within the BP safe zone (e.g.,green) to a different color indicative of a blood pressure outside ofthe BP safe zone (e.g., red). An intermediate color (e.g., yellow ororange) may be utilized to indicate a blood pressure (within the BP safezone) approaching an outer limit out of the BP safe zone. In certainembodiments, the alarm may differentiate between a blood pressure belowthe BP safe zone and a blood pressure above the BP safe zone. Thisdifferentiation may be provided via two different beeps (onerepresentative of blood pressure below the BP safe zone and onerepresentative of blood pressure above the BP safe zone) provided viathe output device 18 (e.g., speaker). The beeps may differ in tones,durations, volume, tunes, or other types of audible features.

The output device 18 may include any device configured to receivesignals (e.g., signals indicative of the autoregulation profile, the BPhistory, the BP signal, the BP safe zone, the TBP, the distance betweenthe current blood pressure and the TBP, the alarm signal, or the like)from the controller 16 and visually and/or audibly output informationindicative of the patient's autoregulation status (e.g., theautoregulation profile, the BP history, the BP signal, the BP safe zone,the TBP, the distance between the current blood pressure and the TBP,the alarm signal, a text message, a color, or the like). For instance,the output device 18 may include a display configured to provide avisual representation of the autoregulation profile, the BP history, theBP signal, the BP safe zone, the TBP, the distance between the currentblood pressure and the TBP, the alarm signal, or the like as determinedby the controller 16. Additionally or alternatively, the output device18 may include an audio device configured to provide sounds (e.g.,spoken message, beeps, or the like) indicative of the patient's theautoregulation profile, the BP history, the BP signal, the BP safe zone,the TBP, the distance between the current blood pressure and the TBP,the alarm signal, or the like. The output device 18 may be any suitabledevice for conveying such information, including a computer workstation,a server, a desktop, a notebook, a laptop, a handheld computer, a mobiledevice, or the like. In some embodiments, the controller 16 and theoutput device 18 may be part of the same device or supported within onehousing (e.g., a specialized computer or monitor).

FIG. 2 illustrates an example of a display 28 of an autoregulationstatus of a patient (e.g., displayed on the output device 18). Thedisplay 28 includes a BP signal area 30 and an autoregulation area 32.As depicted, the BP signal area 30 is located above the autoregulationarea 32. In other embodiments, the BP signal area 30 may be locatedbelow the autoregulation area 32 or both areas 30, 32 may be shown sideby side. The BP signal area 30 includes a plot 34 of a segment of a BPsignal (most recent BP signal) received from the patient. The plot 34includes the blood pressure value (BP) plotted on the vertical axis andtime plotted along the horizontal axis.

The autoregulation area 32 includes autoregulation information such asan autoregulation profile 36, a BP history 38 of the patient, and a BPsafe zone 40. The autoregulation profile 36 is generated based on bloodpressure measurements and autoregulation index values (e.g., HVx, COx,Mx, etc.) obtained from the patient. In the autoregulation profile 36,the autoregulation index values are sorted into bins corresponding todifferent blood pressure ranges as represented by bars 42. Theautoregulation profile 36 includes the autoregulation index valuesplotted along the vertical axis and blood pressures on the horizontalaxis. Bars 42 extending above the horizontal axis indicate positiveautoregulation index values suggesting that the cerebral autoregulationis impaired, while bars 42 extending below the horizontal axis indicatenegative autoregulation index values suggesting that the cerebralautoregulation works properly. In certain embodiments, the bins (or bars42) associated with a positive autoregulation index value may bedisplayed as a different color (e.g., red) than a color (green) of thebins associated with a negative autoregulation index value. As depicted,the number of bins (or bars 42) is 7. However, the number of bins mayvary based on the width of each bin. Each bin may have a width of 5 mmHgunits. In particular, binning measurements may be associated withgrouping certain measurements such that each bin may include orrepresent a certain number of original data measurements. For example,each bin may be representative of a number of original measurements thatfall within a particular interval or width. It should be noted that thewidth or interval of the bin may be a pre-defined value stored withinthe memory device 26, and the width or interval of the bin may be anyvalue greater than 0 mmHg units, between approximately 0 and 3 mmHgunits, between approximately 3 and 5 mmHg units, or greater than 5 mmHgunits. In certain embodiments, the width of each bin may be determinedbased on a quality or an amount of data received from the sensors. Inaddition, each bin may include or represent any number of originalmeasurements or samples. For example, in certain situations, the bin mayrepresent 1-5 samples, 5-10 samples, 10-20 samples, 20-50 samples, ormore than 50 samples. In certain embodiments, the number of samples thateach bin represents may be dependent on the quality of samples obtained,a sampling rate of the sensors, a signal quality metric, and/or anycombination thereof.

The BP safe zone 40 designates a blood pressure range encompassing oneor more of the bins indicative of intact autoregulation. The BP safezone 40 may be overlaid or encompass the corresponding one or more binsof the autoregulation profile 36. In certain embodiments, it may take anumber of minutes to build up a useful picture of the autoregulationfunction. For example, it may take 30 minutes in the operating room or 3to 4 hours in the intensive care unit to experience enough bloodpressure changes to build up the autoregulation profile 36. While theautoregulation profile 36 is being built, the BP safe zone 40 may have acolor (e.g., yellow, see display 49 of FIG. 3) different than a color(e.g., green) of the BP safe zone 40 once enough data has been obtainedto build the autoregulation profile 36. Alternatively, the bars 42, 44within the BP safe zone 40 may have different markings once enough datahas been obtained. For example, in FIG. 2 the bars 42, 44 within the BPsafe zone 40 have no hatching, while the bars 42, 44 on display 49 ofFIG. 3 have hatching. For example, the BP safe zone 40 may be coloredyellow until a preset criterion is reached and change to green uponreaching that criterion. The criterion may be forming enough bars (e.g.,as least 4 bars 42 or any other predetermined number of bars 42).Alternatively, the criterion may be based on an amount of datacollected. For example, a single bar 42 may be sufficient if the bar 42has enough data. In embodiments, where the BP safe zone 40 is colored,the BP safe zone 40 may be transparent enough to visualize the bars 42and their respective color. In some embodiments, a textual indicator(e.g., “Building Autoregulation Profile”, “Autoregulation ProfileComplete”, etc.) may be displayed indicating the status of the buildingof the Autoregulation Profile.

In certain embodiments, if there is insufficient data (e.g.,autoregulation index measurements and blood pressure measurements) fromthe patient, the controller 16 may generate an initial BP safe zone 40utilizing historical population data (e.g., based on patient specificinputs such as age, sex, body mass index, etc.) and/or initiallymeasured baseline physiological parameters (e.g., mean arterial pressure(MAP), heart rate, respiration rate, regional oxygen saturation (rSO₂),etc.) of the patient. Once there is sufficient patient data, thecontroller 16 may generate a patient specific BP safe zone 40 (e.g.,subsequent BP safe zone 40) based on the patient's autoregulation indexmeasurements and blood pressure measurements. The initial BP safe zone40 may have a color (e.g., yellow, see FIG. 3) different than a color(e.g., green, see FIG. 2) of the patient specific BP safe zone 40.

The BP history 38 may be generated based on the blood pressuremeasurements and the autoregulation index values (e.g., HVx, COx, Mx,etc.) obtained from the patient. The BP history 38 may include bins(e.g., bars 44) of blood pressure ranges corresponding to the bins(e.g., bars 42) in the autoregulation profile 36 plotted on a horizontalaxis and a count relating to time spent in the BP safe zone 40 on avertical axis. The count may represent an amount or percentage of timeblood pressure measurements are in the BP safe zone 40, a number oftimes blood pressure measurements are in the BP safe zone 40, or anumber of times blood pressure measurements are out of the BP safe zone40. In certain embodiments, the BP safe zone 40 may also overlay thebins of the BP history 38 that correspond to the bins of theautoregulation profile 36 within the BP safe zone 40. In certainembodiments, the bins (bars 44) of the BP history 38 that correspondwith the bins (e.g., bars 42) having a positive autoregulation indexvalue may be displayed as a different color (e.g., red) than a color(green) of the bins (bars 44) of the BP history 38 that correspond withthe bins (e.g., bars 42) associated with a negative autoregulation indexvalue.

In certain embodiments, an indicator 46 may be displayed in the BPsignal area 30 or the autoregulation area 32 (as depicted in FIG. 2)representing the TBP. The TBP may be received by the controller 16(e.g., via operator input) or may be determined by the controller 16 asdescribed in greater detail below. The indicator 46 may include avertical line (as depicted in FIG. 2), a number (e.g., in mmHg), or apoint. In certain embodiments, an indicator 48 may be displayed in theBP signal area 30 or the autoregulation area 32 (as depicted in FIG. 2)representing a distance of a current blood pressure measurement of thepatient from the TBP. In certain embodiments, the indicator 48 mayinclude a blip bar (as depicted in FIG. 2) that increases (e.g., fillsup) as the distance increases between the current blood pressuremeasurement and the TBP or decreases (e.g., empties) as the distancedecreases between the current blood pressure measurement and the TBP.Alternatively, the indicator 46 of the TBP may undergo a gradiated colorchange (e.g., from green (smaller distance) to amber (intermediatedistance) to red (greater distance)) as the distance between the currentblood pressure and the TBP changes.

In certain embodiments, if the current blood pressure of the patientfalls outside of the BP safe zone 40, the controller 16 may provide analarm (e.g., visual indication) via the display 28. In certainembodiments, the alarm may be provided via the flashing of portions ofthe display 28 (e.g., the autoregulation profile 36, the BP safe zone40, the BP history 38, and/or the BP signal 34). The alarm may also beprovided via changing a color of the BP safe zone 40 indicative of ablood pressure within the BP safe zone 40 (e.g., green) to a differentcolor indicative of a blood pressure outside of the BP safe zone 40(e.g., red). An intermediate color (e.g., yellow or orange) may beutilized to indicate a blood pressure (within the BP safe zone 40)approaching an outer limit out of the BP safe zone 40. In certainembodiments, the alarm may differentiate between a blood pressure belowthe BP safe zone 40 and a blood pressure above the BP safe zone 40utilizing different colors for the BP safe zone 40. In certainembodiments, a textual alarm may be provided on the display 28 (e.g.,“Blood Pressure Outside BP Safe Zone”, “Blood Pressure Approaching BeingOutside the BP Safe Zone”, etc.).

FIG. 4 is a process flow diagram of a method 50 of monitoringautoregulation that includes designating a BP safe zone. The method 50includes various steps represented by blocks. The method 50 may beperformed as an automated procedure by a system, such as system 10. Forexample, some or all of the steps of the method 50 may be implemented bythe controller 16 (e.g., the processor 24 of the controller 16).Although the flow chart illustrates the steps in a certain sequence, itshould be understood that the steps may be performed in any suitableorder, certain steps may be carried out simultaneously, and/or certainsteps may be omitted, where appropriate. In addition, insofar as stepsof the method 50 disclosed herein are applied to the received signals,it should be understood that the received signals may be raw signals orprocessed signals. That is, the method 50 may be applied to an output ofthe received signals.

In step 52, the controller 16 may receive physiological signals. Forexample, the controller 16 may receive the blood pressure signal (e.g.,arterial blood pressure signal). In some embodiments, the controller 16may receive the blood pressure signal from the blood pressure sensor 12,as set forth above. In some embodiments (if COx is utilized for theautoregulation index), the controller 16 may receive the oxygensaturation signal (e.g., regional oxygen saturation signal) from theregional oxygen saturation sensor 14. In some embodiments (if HVx isutilized for the autoregulation index), the controller 16 may receivethe blood volume signal from the regional oxygen saturation sensor 14.

In step 54, the controller 16 determines a correlation-based measureindication of autoregulation (e.g., autoregulation index values such asHVx, COx, Mx, etc.) based on the received physiological signals. In step56, the controller 16 generates the autoregulation profile based on theautoregulation index values of the correlation based measure and theblood pressure signal. As noted above, the autoregulation profileincludes the autoregulation index values sorted into bins correspondingto different pressure ranges. In step 58, the controller 16 designates ablood pressure range for the BP zone. As noted above, in certainembodiments, if there is insufficient patient data (e.g., autoregulationindex measurements and blood pressure measurements) of the patient, thecontroller 16 may generate an initial BP safe zone utilizing historicalpopulation data (e.g., based on patient specific inputs such as age,sex, body mass index, etc.) and/or initially measured baselinephysiological parameters (e.g., mean arterial pressure (MAP), heartrate, respiration rate, regional oxygen saturation (rSO₂), etc.) of thepatient. Once there is sufficient patient data, the controller 16 maygenerate a patient specific BP safe zone (e.g., subsequent BP safe zone)based on the patient's autoregulation index measurements and bloodpressure measurements.

In step 60, in certain embodiments, the controller 16 determines the TBPas described in greater detail below. Alternatively, in otherembodiments, in step 62, the controller 16 receives the TBP. In step 64,the controller 16 provides one or more signals to display theautoregulation profile, the BP signal, the BP history, the TBP, and/orthe BP safe zone on the output device 18 (e.g., display) as describedabove. In step 66, the controller 16 compares the patient's currentblood pressure (derived from the blood pressure signal) to the TBP. Instep 68, the controller 16 provides a signal to display an indication ofa distance between the current blood pressure and the TBP. As notedabove, a blip bar may be utilized or an indicator of the TBP may undergoa gradiated color change.

In step 70, the controller 16 compares the patient's current bloodpressure (derived from the blood pressure signal) to the BP safe zone.In step 72, if the patient's current blood pressure is outside of the BPsafe zone, the controller 16 provides an alarm signal to the outputdevice 18 (e.g., display and/or speaker). The alarm may include a visualor audible alarm. In certain embodiments, the alarm may be provided viathe flashing of portions of the display (e.g., the autoregulationprofile, the BP safe zone, the BP history, and/or the BP signal). Thealarm may also be provided via changing a color of the BP safe zoneindicator indicative of a blood pressure within the BP safe zoneindicator (e.g., green) to a different color indicative of a bloodpressure outside of the BP safe zone indicator (e.g., red). Anintermediate color (e.g., yellow or orange) may be utilized to indicatea blood pressure (within the BP safe zone) approaching an outer limitout of the BP safe zone. In certain embodiments, the alarm maydifferentiate between a blood pressure below the BP safe zone and ablood pressure above the BP safe zone utilizing different colors for theBP safe zone. In certain embodiments, a textual alarm may be provided onthe display (e.g., “Blood Pressure Outside BP Safe Zone”, “BloodPressure Approaching Being Outside the BP Safe Zone”, etc.). In otherembodiments, the alarm may differentiate between a blood pressure belowthe BP safe zone and a blood pressure above the BP safe zone utilizingtwo different beeps (one representative of blood pressure below the BPsafe zone and one representative of blood pressure above the BP safezone) via a speaker. The beeps may differ in tones, durations, volume,tunes, or other types of audible features.

FIG. 5 is a process flow diagram of a method 74 of monitoringautoregulation that includes determining how to designate a bloodpressure safe zone. The method 74 includes various steps represented byblocks. The method 74 may be performed as an automated procedure by asystem, such as system 10. For example, some or all of the steps of themethod 74 may be implemented by the controller 16 (e.g., the processor24 of the controller 16). Although the flow chart illustrates the stepsin a certain sequence, it should be understood that the steps may beperformed in any suitable order, certain steps may be carried outsimultaneously, and/or certain steps may be omitted, where appropriate.In addition, insofar as steps of the method 74 disclosed herein areapplied to the received signals, it should be understood that thereceived signals may be raw signals or processed signals. That is, themethod 74 may be applied to an output of the received signals.

In step 76, the controller 16 may receive physiological signals. Forexample, the controller 16 may receive the blood pressure signal (e.g.,arterial blood pressure signal). In some embodiments, the controller 16may receive the blood pressure signal from the blood pressure sensor 12,as set forth above. In some embodiments (if COx is utilized for theautoregulation index), the controller 16 may receive the oxygensaturation signal (e.g., regional oxygen saturation signal) from theregional oxygen saturation sensor 14. In some embodiments (if HVx isutilized for the autoregulation index), the controller 16 may receivethe blood volume signal from the regional oxygen saturation sensor 14.

In step 78, the controller 16 determines a correlation-based measureindication of autoregulation (e.g., autoregulation index values such asHVx, COx, Mx, etc.) based on the received physiological signals. In step80, the controller 16 generates the autoregulation profile based on theautoregulation index values of the correlation based measure and theblood pressure signal. As noted above, the autoregulation profileincludes the autoregulation index values sorted into bins correspondingto different pressure ranges.

In step 82, the controller 16 determines if there is sufficient data(e.g., autoregulation index measurements and blood pressuremeasurements) of the patient to designate a patient specific BP safezone. If there is insufficient patient data (e.g., autoregulation indexmeasurements and blood pressure measurements) of the patient, in step84, the controller 16 may designate an initial BP safe zone utilizinghistorical population data (e.g., based on patient specific inputs suchas age, sex, body mass index, etc.) and/or initially measured baselinephysiological parameters (e.g., mean arterial pressure (MAP), heartrate, respiration rate, regional oxygen saturation (rSO₂), etc.) of thepatient. If there is sufficient patient data or once there is sufficientpatient data, in step 86, the controller 16 may generate a patientspecific BP safe zone (e.g., subsequent BP safe zone) based on thepatient's autoregulation index measurements and corresponding bloodpressure measurements. In step 88, the controller 16 provides one ormore signals to display the autoregulation profile, the BP signal, theBP history, the TBP, and/or the BP safe zone on the output device 18(e.g., display) as described above. In certain embodiments, thecontroller 16 may perform additional steps such as those described abovein FIG. 5.

As mentioned above, the TBP may be determined by the controller 16, inparticular, utilizing an rSO₂-BP curve. In particular, it may bedesirable to determine the TBP somewhere within the region defined bythe LLA and ULA. FIG. 6 is an example of a graph 90 illustrating anrSO₂-BP curve 92 derived from regional oxygen saturation values on thevertical axis and blood pressure (e.g., arterial blood pressure) values(e.g., having a target blood pressure derived from the rSO₂-BP curve 92)on the horizontal axis. As depicted, the rSO₂-BP curve 92 is an idealcurve. In particular, the curve 92 includes (from left to right) apositive gradient portion 94 (e.g., indicative of impairedautoregulation), a horizontal plateau 96 (e.g., indicative of intactautoregulation), and another positive gradient portion 98 (e.g.,indicative of impaired autoregulation). The LLA (represented by line100) separates the positive gradient portion 94 from the horizontalplateau 96. The ULA (represented by line 102) separates the horizontalplateau 96 from the positive gradient portion 98. As described above,cerebral autoregulation occurs over a range of blood pressures betweenthe LLA and the ULA. As depicted in FIG. 6, the controller 16 determinesthe TBP by designating a point (represented by line 104) equidistantbetween the LLA and ULA along the curve 92.

In certain embodiments, the controller 16 determines the TBP bydesignating a point nearer the ULA if the clinical consequences ofdropping below the LLA are more severe for the patient than if the ULAis exceeded. In other embodiments, the controller 16 determines the TBPby designating a point nearer the LLA if the clinical consequences ofexceeding the ULA are more severe for the patient than dropping belowthe LLA.

In certain embodiments, gradients of the curve 92 may be utilized indetermining the TBP. FIG. 7 is an example of a graph 106 illustratingthe rSO₂-BP curve 92 and the utilization of gradients to determine theTBP. The controller 16 may determine a gradient portion, m_(l), for thepositive gradient portion 94 of the curve 92. The controller 16 may alsodetermine a gradient portion, m_(u), for the positive gradient portion98 of the curve 92. In certain embodiments, the controller 16 weightsthe TBP towards a higher gradient portion as it may be better defined interms of the rSO₂-BP relationship. For example, the TBP (represented byline 104) may be shifted toward ULA since m_(u) has a higher gradientthan m_(l) as depicted in FIG. 7. In other embodiments, the controller16 weights the TBP towards a lower gradient portion as deviations fromthe TBP during a procedure may have less effect on the cerebraloxygenation. For example, the TBP may be shifted toward the LLA sincem_(l) may have a higher gradient than m_(u).

FIG. 8 is a process flow diagram of a method 108 of determining the TBPutilizing characteristics (e.g., gradients or error size) of the rSO₂-BPcurve 92 derived from regional oxygen saturation values and bloodpressure values. The method 108 includes various steps represented byblocks. The method 108 may be performed as an automated procedure by asystem, such as system 10. For example, some or all of the steps of themethod 108 may be implemented by the controller 16 (e.g., the processor24 of the controller 16). Although the flow chart illustrates the stepsin a certain sequence, it should be understood that the steps may beperformed in any suitable order, certain steps may be carried outsimultaneously, and/or certain steps may be omitted, where appropriate.In addition, insofar as steps of the method 108 disclosed herein areapplied to the received signals, it should be understood that thereceived signals may be raw signals or processed signals. That is, themethod 108 may be applied to an output of the received signals.

In step 110, the controller 16 may receive the blood pressure signal(e.g., arterial blood pressure signal) and the regional oxygensaturation signal. In some embodiments, the controller 16 may receivethe blood pressure signal from the blood pressure sensor 12, as setforth above. In some embodiments, the controller 16 may receive theregional oxygen saturation signal from the regional oxygen saturationsensor 14. In step 112, the controller 16 generates the rSO₂-BP curve(e.g., rSO2-BP curve 92) from the blood pressure signal and the regionaloxygen saturation signal. In step 114, the controller 16 may determinethe LLA and ULA from the rSO₂-BP curve. In step 116, the controller 16may determine a blood pressure range between the LLA and ULA. In step118, the controller 16 may determine the gradients, m_(u) and m_(l),from the rSO₂-BP curve.

In step 120, the controller 16 may determine the TBP utilizing one ormore equations. For example, in embodiments where the TBP is weightedtowards the lower gradient, the controller 16 may utilize the followingequation:TBP=LLA+RANGE×(m _(u)/(m _(u) +m _(l))),  (1)where RANGE=ULA−LLA. In embodiments where the TBP is weighted towardsthe higher gradient, the controller may utilize the following equation:TBP=ULA−RANGE×(m _(u)/(m _(u) +m _(l))).  (2)

As described below, other characteristics of the rSO₂-BP curve may beutilized in determining the TBP. In step 122, the controller 16 mayprovides a signal to the output device 18 to display the TBP asdescribed above.

In other embodiments, error bars associated with the curve may beutilized by the controller 16 to determine the TBP. FIG. 9 is an exampleof a graph 124 illustrating the rSO₂-BP curve 92 derived from regionaloxygen saturation values and blood pressure values (e.g., having the TBPderived from errors associated with the rSO₂-BP curve 92). As depicted,the curve 92 may include error bars 126 associated with differentregions of the curve 92. From these error bars 26, a characteristic sizeof the error, E, may be derived (e.g., E_(l) for region positivegradient region 94 and E_(u) for positive gradient portion 98) for eachregion of the curve 92. E_(l) and E_(u) may be determined utilizing avariety of statistics (e.g., standard deviation, mean absolutedeviation, mediation absolute deviation, etc.). In embodiments where theTBP is weighted towards the error bars 26 associated with the region 94below the LLA, the controller 16 may utilize the following equation:TBP=LLA+RANGE×(E _(l)/(E _(u) +E _(l))).  (3)

In embodiments where the TBP is weighted towards the error bars 26associated with the region 98 about the ULA, the controller 16 mayutilize the following equation:TBP=ULA−RANGE×(E _(l)/(E _(u) +E _(l))).  (4)

In certain embodiments, the rSO₂-BP curve may not be ideal fordetermining the TBP. FIG. 10 is an example of a graph 128 illustrating anon-ideal rSO₂-BP curve 130 derived from regional oxygen saturationvalues and blood pressure values. The curve 130 may include smoothchanges as depicted in FIG. 10. In certain embodiments, a secondderivative may be taken from the curve 130 to a search for a zerorepresenting the point of inflection. The point of inflection 132 of thecurve 130 may be utilized by the controller as the TBP.

In certain embodiments, more complex functions (e.g., time-tangentialfunctions, artificial neural network, etc.) may be utilized by thecontroller 16 to determine the TBP. In other embodiments, patientspecific information (age sex, BMI, etc.) may be utilized as inputs bythe controller 16 to determine the TBP.

While the disclosure may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the embodiments provided hereinare not intended to be limited to the particular forms disclosed.Rather, the various embodiments may cover all modifications,equivalents, and alternatives falling within the spirit and scope of thedisclosure as defined by the following appended claims. Further, itshould be understood that certain elements of the disclosed embodimentsmay be combined or exchanged with one another.

What is claimed is:
 1. A monitor for monitoring autoregulation, themonitor comprising: a display; a memory encoding one or moreprocessor-executable instructions; and one or more processors configuredto access and execute the one or more instructions encoded by thememory, wherein the instructions, when executed, cause the one or moreprocessors to: receive one or more physiological signals from a patient;determine a correlation-based measure indicative of an autoregulation ofthe patient based on the one or more physiological signals; generate anautoregulation profile of the patient based on autoregulation indexvalues of the correlation-based measure, wherein the autoregulationprofile comprises the autoregulation index values sorted into binscorresponding to different blood pressure ranges; designate a bloodpressure range encompassing one or more of the bins as a blood pressuresafe zone indicative of intact autoregulation; provide a first signal tothe display to display the autoregulation profile and a first indicatorof the blood pressure safe zone; and provide a second signal to thedisplay to display a second indicator of a target blood pressure withinthe blood pressure safe zone for the patient.
 2. The monitor of claim 1,wherein the correlation-based measure is one of a cerebral oximetryindex, a hemoglobin volume index, or a mean velocity index.
 3. Themonitor of claim 1, wherein the one or more instructions, when executed,cause the one or more processors to: receive patient specific inputs,the patient specific input being physical characteristics of thepatient, wherein the instructions to designate the blood pressure rangeencompassing one or more of the bins as the blood pressure safe zoneindicative of intact autoregulation comprise instructions to designatethe blood pressure range encompassing one or more of the bins as aninitial blood pressure safe zone indicative of intact autoregulationutilizing at least historical population data based on the patientspecific inputs, and wherein the instructions to provide the firstsignal to the display comprise instructions to provide a signal todisplay an indicator of the initial blood pressure safe zone.
 4. Themonitor of claim 3, wherein the instructions to designate the bloodpressure range encompassing one or more of the bins as the initial bloodpressure safe zone indicative of intact autoregulation compriseinstructions to designate the blood pressure range as the initial bloodpressure safe zone utilizing both the historical population data basedon the patient specific inputs and initially measured baselines ofphysiological parameters of the patient.
 5. The monitor of claim 3,wherein the one or more instructions, when executed, cause the one ormore processors to: determine if there is sufficient data within theautoregulation profile to designate a patient-specific blood pressuresafe zone; in response to determining that there is sufficient data,subsequently designate the blood pressure range encompassing one or moreof the bins as a subsequent patient specific blood pressure safe zoneindicative of intact autoregulation utilizing the autoregulation indexvalues and corresponding blood pressure levels; and provide a thirdsignal to the display to display an indicator of the subsequent patientspecific blood pressure safe zone.
 6. The monitor of claim 5, whereinthe indicator of the initial blood pressure safe zone comprises a firstcolor, and wherein the indicator of the subsequent patient specificblood pressure safe zone comprises a second color different from thefirst color.
 7. The monitor of claim 1, wherein the one or moreinstructions, when executed, cause the one or more processors to: changea color of the second indicator displayed on the display based on adistance of a current blood pressure of the patient derived from thetarget blood pressure; or change a level of a blip bar displayed on thedisplay based on the distance of the current blood pressure of thepatient derived from the target blood pressure.
 8. The monitor of claim1, wherein the one or more instructions, when executed, cause the one ormore processors to receive a user input of the target blood pressure. 9.The monitor of claim 1, wherein the one or more physiological signalscomprise a regional oxygen saturation signal and a blood pressuresignal, wherein the instructions to generate the autoregulation profilecomprise instructions to generate a curve from the regional oxygensaturation signal and the blood pressure signal, and wherein theinstructions to designate the blood pressure safe zone compriseinstructions to: determine both a lower limit (LLA) and an upper limit(ULA) of autoregulation from the curve; and determine the target bloodpressure based on the curve.
 10. The monitor of claim 9, wherein theinstructions to determine the target blood pressure compriseinstructions to designate a point equidistant between the LLA and ULA asthe target blood pressure.
 11. The monitor of claim 9, wherein the oneor more instructions, when executed, cause the one or more processorsto: determine a first gradient of the curve at a first blood pressureportion of the curve lower than the LLA; and determine a second gradientof the curve at a second blood pressure portion of the curve higher thanthe ULA, wherein the instructions to determine the target blood pressurecomprise instructions to determine the target blood pressure based onthe first gradient, the second gradient, or a combination thereof. 12.The monitor of claim 9, wherein the instructions to determine the targetblood pressure comprise instructions to designate a point of inflectionof the curve as the target blood pressure.
 13. The monitor of claim 1,wherein the one or more instructions, when executed, cause the one ormore processors to provide a third signal to the display or other outputdevice to provide an audible or visual indication that a current bloodpressure of the patient is outside the blood pressure safe zone.
 14. Themonitor of claim 13, wherein the audible or visual indication comprisesa first audible or visual indication that indicates that the currentblood pressure is higher than the blood pressure safe zone and a secondaudible or visual indication that the current blood pressure is lowerthan the blood pressure safe zone, and wherein the first audible orvisual indication is different from the second audible or visualindication.
 15. The monitor of claim 1, wherein the instructions toprovide the first signal to the display comprise instructions to causethe display to flash the autoregulation profile and the first indicatorof the blood pressure safe zone on and off.
 16. The monitor of claim 1,wherein the instructions to provide the first signal to the displaycomprise instructions to provide the first signal to the display todisplay a blood pressure history of the patient, wherein the bloodpressure history depicts an amount of time blood pressure measurementswithin the bins are within the blood pressure safe zone.
 17. The monitorof claim 16, wherein the first indicator of the blood pressure safe zoneoverlays a portion of the autoregulation profile corresponding to theblood pressure safe zone.
 18. A method for monitoring autoregulation,the method comprising: receiving, by one or more processors executingone or more instructions encoded on a memory, one or more physiologicalsignals from a patient; determining, by the one or more processors, acorrelation-based measure indicative of an autoregulation of the patientbased on the one or more physiological signals; generating, by the oneor more processors, an autoregulation profile of the patient based onautoregulation index values of the correlation-based measure, whereinthe autoregulation profile comprises the autoregulation index valuessorted into bins corresponding to different blood pressure ranges;designating, by the one or more processors, a blood pressure rangeencompassing one or more of the bins as a blood pressure safe zoneindicative of intact autoregulation; providing, by the one or moreprocessors and to a display, a signal to display the autoregulationprofile and a first indicator of the blood pressure safe zone; andproviding, by the one or more processors and to the display, a secondsignal to display a second indicator of a target blood pressure withinthe blood pressure safe zone for the patient.
 19. A monitor formonitoring autoregulation, the monitor comprising: a display; a memoryencoding one or more processor-executable instructions; and one or moreprocessors configured to access and execute the one or more instructionsencoded by the memory, wherein the instructions, when executed, causethe one or more processors to: receive one or more physiological signalsfrom a patient; determine a correlation-based measure indicative of anautoregulation of the patient based on the one or more physiologicalsignals; generate an autoregulation profile of the patient based onautoregulation index values of the correlation-based measure, whereinthe autoregulation profile comprises the autoregulation index valuessorted into bins corresponding to different blood pressure ranges;determine if there is sufficient data within the autoregulation profileto designate a patient-specific blood pressure safe zone; in response todetermining that there is sufficient data, designate a blood pressurerange encompassing one or more of the bins as a patient-specific bloodpressure safe zone indicative of intact autoregulation utilizing theautoregulation index values and corresponding blood pressure levels; andprovide a first signal to the display to display the autoregulationprofile and a first indicator of the patient-specific blood pressuresafe zone.
 20. The monitor of claim 19, wherein the one or moreinstructions, when executed, cause the one or more processors to:receive patient specific inputs, the patient specific inputs beingphysical characteristics of the patient; in response to determining thatthere is insufficient data, designate the blood pressure rangeencompassing one or more of the bins as an initial blood pressure safezone indicative of intact autoregulation utilizing at least historicalpopulation data based on the patient specific inputs; and provide asecond signal to the display to display an indicator of the initialblood pressure safe zone.
 21. The monitor of claim 1, wherein the one ormore instructions, when executed, cause the one or more processors toprovide a third signal to the display or another output device toprovide a visual or audible indication of a distance the current bloodpressure is from the target blood pressure.